Mixing apparatus for test tubes

ABSTRACT

Devices and methods for the mixing of liquid samples which comprise means for performing the mixing, including a resting phase during the mixing cycle.

The present invention concerns a test tube mixing apparatus

When obtaining blood samples, the blood is transferred from the patientto a test tube through a cannula to prevent the blood from beingunusable it must immediately be mixed with an anticoagulating agent (ase.g. sodium citrate) which stops the otherwise immediately initiatedcoagulation of the blood. For the mixing to be effective a test tube,e.g. a vacuum tube, has to be slowly turned at least ten times for theair bubble which is present in the test tube to be able to pass thewhole length of the tube. The anticoagulating agent contents within thetube then passes and mixes with the blood contents of the tube. Themixing has to date in accomplished manually, which is carried out insuch a way that the sampling personell by hand turns the tube theprescribed at least ten times, controlling at the same time that the airbubble each time passes the whole length of the tube, considering thatthe personnel taking samples often has to collect samples from a largenumber of patients, the manual mixing has shown to be an ergonomicproblem in that sence that the frequent repeating turning movement isvery straining for the wrist and the shoulders. At the same time ascarrying out the mixing, the sample collector is also occupied withlooking after the patient and possibly filling further test tubes. Sincethe quality of the sample is entirely dependent on the mixing beingcarried out in a correct manner, lack of concentration of the personnelleads to unusability of a large number of samples, which therefore hasto be obtained again. The reason for this may be that the mixing wasinitiated too late, that the mixing movement was carried out too fast orthat the mixing was not carried out a sufficient number of cycles. Takentogether this leads to a deterioration of the quality of the resultsfrom the analysis or the unusefulness of the sample.

So called rocking mixer devices for test tubes are previously known,c.f. U.S. Pat. No. 3,261,594. This rocking device is, however, firstlysuited for mixing immediately prior to analysis of blood samples wherethe blood cells have been compacted at the bottom of the test tube afterstoring or transport. For this object the mixing frequency anddurability are not particularly critical, why the known device may beinvolved with parameters that are unsuitable for the mixing in of ananti-coagulating agent. The presence of external means for regulatingthe frequency, that are present in this device, further comprises a riskfactor to the extent that the operator may alter a carefully testedadjustment. Besides, it does not give any indication of a sufficientmixing being carried out as rocking mixer devices of this kind work withan uninterrupted oscillating movement. This known rocking device isfurther because of its design with e.g. trays for the tubes, directlyunsuitable for use at the sample collecting occasion.

In another previously known mixing device the tubes are fixed in asupport which is brought to perform a continously rotating movement.This device is besides being impaired with previously known drawbacksalso time consuming to handle and is not usable at the sample collectingoccasion.

It is an aim with this invention to overcome the above problems and toprovide a mixing device for test tubes, which is simple and flexible tohandle, which subject the tubes to an accurate mixing movement, gives asafe indication of the mixing process being effected and is possible torealise in such a size that it may be put on a sample collectingcarriage and is thereby easily brought by the sample collectingpersonell on a sample collecting round, preferably without anyconnection to an external source of current, and is usable directly atthe sample collecting occasion.

These and also other aims are achieved with a mixing device inaccordance with the features of the present invention.

By thus the mixing tray for receiving the test tubes being subjected toa rocking motion of a prescribed frequency and with a prescribed numberof oscillations when started, it is achieved that test tubes that areplaced on the mixing tray immediately after the sample collectingoccasion are safely subjected to the prescribed mixing process.

Further advantages are achieved by the features according to thedependent claims.

A particularly advantageous mixing movement is achieved when arelatively fast rocking phase is combined with a resting period, wherethe air bubble being present within the tube has the time to pass theentire length of the tube.

The invention will now be described in greater detail with reference toan embodiment and appended drawings of which

FIG. 1 shows a mixing device according to the invention in a front view,

FIG. 2 shows the mixing device according to FIG. 1 in a side view, and

FIG. 3 shows, in schematic form, the intermittent rocking drive unitdrivingly coupled to the mixing tray.

The mixing device 1 according to FIGS. 1, 2 and 3 comprises a base 2within which a driving means in the form of an electric motor 22 iscontained. Within the base there are also comprised control circuitry 24for controlling the mixing movement as well as a current source 26 ase.g. a rechargeable battery. Above the base a mixing tray is fastened,which is connected to the drive unit in the base 2 through a drivingyoke 4, the substantially horizontal portion of which is fixed to themixing tray 3. The vertical portions of the driving yoke 4 removablycooperate with slots in driving discs 6 being provided on each side ofthe base, said discs being connected to the drive unit by means of adrive shaft 5. Through the removable cooperation between the drivingyoke 4 and the driving discs 6, it is achieved that the driving yoke 4together with the mixing tray 3, is simply removable from the base 2,which facilitates cleaning and transport of the device. The mixing tray3 comprises on its upper surface a number of grooves 7 for receivingtest tubes 8. The width and the length of the grooves are adjusted sothat the mixing device 1 may be used for all test tubes that areavailable on the market. The test tube 8 shown in FIGS. 1 and 2 is ofvacuum type and consists of a glass tube with a plug 11 in its upperportion. Appropriately filled with blood and anticoagulating agent thetube 8 displays a liquid surface 9 immediately below the plug 11,whereby an air bubble 10 is present between the liquid surface and theplug. As is evident from FIG. 2, the mixing tray 3 is comprised withtube stops 12a and 12b at its ends to prevent the tube from gliding offfrom the mixing tray in its longitudinal direction. The grooves 7 end ata portion from the upper tube stop 12a in the figure, whereby a recess15 is formed, which facilitates putting in and taking out of test tubesfrom the mixing tray.

The method of working of the mixing device 1 is as follows. Immediatelyafter that a test tube 8 has been filled with blood from a patient andanticoagulating agent, it is placed on the mixing tray 3 whereafter thesample collector presses the start button 13. The drive unit will thensubject the mixing tray 3 to a rocking movement from the position shownin FIG. 2, where the mixing tray is inclined to the left an angle α tothe horizontal plane to a position where the mixing tray is inclinedwith an angle at the other direction (the angel β not shown in thefigure), which may be different from or equal to α. The angles may mechosen within the area between 15° and 60°, but are preferably between25° and 45°. The rocking frequency may easily be tested concerning e.g.the type of test tube to be used, but should as a matter of precautionbe so low that sufficient mixing is acheived for the most difficult tomix test tubes, whereby the air bubble being present in the tubes willsafely pass the entire length of the tube also for thin long tubes. Thefrequency will then be in the order of 0.2 to 2 Hz. Particularly goodmixing is achieved when the mixing tray stops and rests a certain amountof time in every end position, whereby the air bubble gives theopportunity to rise to the at present upper part of the tube in theresting periods. To achieve an adequate mixing movement where the abovementioned air bubble passes the entire length of all possible tubes inevery oscillation, all parameters: frequency, angles of inclination αand β and resting period must be adjusted to each other for the mostunfavourable condition. Preferably the position shown in the figures,with an inclination of the mixing tray an angle α is an initialposition, which is taken by the tray 3 when it stops.

The number of oscillations being carried out by the mixing device mayalso be tested, but is preferably within the area around 8-12.Preferably the control circuitries of the mixing device are designed insuch a way that a start signal leads to the prescribed number ofoscillations being carried out thereafter even if the signal is givenwhile the device is already started. In this way it is unnecessary towait for a completed mixing cycle since there is no risk of subjecting atube to mixing too long, only by letting it mix for a too short a time.To further guarantee the function of the apparatus the base 2 preferablyis comprised with an indicator lamp 14 in the form of e.g. a lightdiode, for indication of low charging level of the battery in good timebefore the stand still of the apparatus due to a discharged battery. Thedevice may also be provided with a circuit for delivering a light or asound signal indicating a completed mixing cycle. To handle e.g. leakingtubes, manual quick-stop may be arranged in the circuitry. To indicatemalfunction it is preferred to have control means delivering e.g. anintermittent light signal when the mixing is not completed.

The invention is not limited to the above described embodiment, but onlyto what is stated in the claims. Thus the mixing tray 3 may be subjectedto a rocking movement of the above mentioned kind by means of any othersuitable transmission. The removability of the mixing tray can furtherbe achieved in any other suitable manner, e.g. through loosenableconnection with respect to the driving yoke, which in itself ispermanently fixed to the base.

It is also possible that for a elimination of missing delivering of thestart signal, the drive unit is started by a test tube 8 being placed ina groove 7 of the mixing tray 3. In this case the mixing tray may beprovided with any kind of sensing element, which transmits a startsignal to the drive unit. In a preferred embodiment the test tubes areprovided with a detectable, e.g. magnetized, element, the presence ofwhich is detected by a detecting device on the mixing tray, which thensends a start signal to the drive unit. Said element may be integralwith an identification label or put on the test tube in any other way,e.g. as a piece of magnetic tape. The detecting device on the mixingtray may be passive, and thus not consume any energy. If, however, thedetecting element is active with a certain current consumption, thedevice may be provided with control and time circuits aiming to limitthe time when the device is in a stand-by position and thereby limit thecurrent consumption.

Alternatively a start signal may be given by pressing down of the mixingtray, the driving yoke or corresponding elements in connection with theplacing of the test tube on the mixing tray.

I claim:
 1. A mixing device for test tubes, comprising a base with anintermittent rocking drive unit arranged therein and a mixing tray, forreceiving test tubes, movably mounted to said base, said intermittentrocking drive unit comprising intermittent drive control circuitry, amotor coupled to and controlled by the control circuitry, the motordrivingly coupled to the mixing tray, said mixing tray being driven bysaid intermittent rocking drive unit which subjects said mixing tray toan intermittent rocking movement, wherein said intermittent rockingdrive unit is constructed and arranged to perform said intermittentrocking movement with a prescribed frequency and a prescribed number ofoscillations when started, with a resting period at each end position ofsaid intermittent rocking movement so that each test tube is subjectedto a prescribed mixing process.
 2. The mixing device of claim 1, whereinthe length of said resting period is adjustable and adapted to saidprescribed frequency and to the angles of inclination of the mixing trayin said end positions.
 3. The mixing device of claim 1, wherein saidintermittent rocking drive unit includes driving discs adapted to move adriving yoke which is mounted on either side of said base, wherein saiddriving yoke is fastened to said mixing tray.
 4. The mixing device ofclaim 1, wherein the drive unit is adapted to perform the prescribednumber of oscillations after a start signal has been given, wherein saidstart signal is given before or after said rocking motion commences. 5.The mixing device of claim 1, wherein said mixing tray has a groovedupward surface sized to receive said test tubes.